Tectonics in the Tropics Trigger the Ice Ages on Earth

March 26, 2019

Image Credits: The Independent

Scientists have figured out the likely trigger for the three ice ages, which occurred in the last 540 million years.

The term ‘Ice Age’ refers to a period during which global
temperatures fall drastically to produce extensive glaciers and ice sheets that
stretch well beyond their polar caps. According to a recent study, tectonics in
the tropics are the likely triggers for these ice ages. A phenomenon, known as ‘Arc-continent Collisions’, is held
responsible for these extremely cold periods as they expose tens of thousands
of kilometers of oceanic rock to a tropical environment. Basically, oceanic
plates rode up over continental plates during this process, following a series
of tectonics near the Equator of the planet. Olivier Jagoutz, an Associate
Professor in the Department of Earth, Atmospheric, and Planetary Sciences at MIT,
talked about that and said,

“We think that arc-continent collisions at low latitudes are the trigger for global cooling. This could occur over 1-5 million square kilometers, which sounds like a lot. But in reality, it’s a very thin strip of Earth, sitting in the right location that can change the global climate.”

The researching team proposed that
the heat and humidity of the tropics could be the reason which triggers a
chemical reaction between the atmosphere and the rocks. They specifically mentioned
that Magnesium and Calcium can pull out Carbon Dioxide permanently from the atmosphere
by reacting with the greenhouse gas. When this process continues to occur over
millions of square kilometers, sufficient Carbon Dioxide is extracted from the
atmosphere to cause cooling at a global scale. This ultimately leads to extreme
spells of low temperatures called ‘Ice Ages’.

Sutures and Ice Ages

The suture is a fault zone along which the continental and oceanic
plates collide. A number of mountain ranges, including the Himalayas, have
several sutures that have migrated from their original positions over a period
of millennia. The researching team of Jagoutz observed two sutures of the Himalayas in 2016 and found that both of them
have a common tectonic migration. One of them was created 80 million years ago
when Gondwana (supercontinent) moved north while the second suture is around 50
million years old.

On both occasions, global
atmospheric cooling events preceded the arc-continent collisions by millions of
years and they occurred in tropical zones near the equator. Researchers
analyzed the rate of reaction between Carbon Dioxide and Ophiolites (oceanic
rocks) to conclude that both of these sutures could have eliminated enough gas
from the atmosphere to trigger the corresponding ice ages. Surprisingly, it was found
that the same process is likely responsible for ending these ice ages as the
oceanic rock erodes away with time and the new rock doesn’t consume that much Carbon Dioxide. Jagoutz
referred to that in the following words:

“We showed that this process can start and end glaciation. Then we wondered, how often does that work? If our hypothesis is correct, we should find that for every time there’s a cooling event, there are a lot of sutures in the tropics.”

Confirmation of the Hypothesis

In order to be certain about
their theory, the researching team performed an extensive study to figure out the
locations of all the major suture zones on Earth. Once their data was complete,
they used a computer simulation to reconstruct the movement of continental and oceanic
plates and these suture zones. This journey towards the past allowed them to
determine the origin of these sutures. It was observed that major sutures were
formed (in the tropics) in three different phases in the last 540 million years
and all of these periods coincided with one of the famous ice ages. Similarly,
simulations showed that no ice ages were possible when major suture zones were
outside of the tropics. Jagoutz acknowledged that by saying,

“We found that every time there was a peak in the suture zone in the tropics, there was a glaciation event. So every time you get, say, 10,000 kilometers of sutures in the tropics, you get an ice age.”

The study published in the
journal ‘Science’ also revealed that a major suture zone, which is spanning
over an area of about 10,000 kilometers, is still active today in Indonesia.
Jagoutz suggested that it is very much possible that the appearance of extensive
ice sheets at the poles could be an indication of another ice age.

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